In automotive production lines, individual workpieces, such as automotive body panels, frame components, etc., may be transported between workstations where selected operations, such as welding or other joining operations, are performed by workers, robots, or other processing equipment. Transporting individual workpieces to, and accurately placing the workpieces at, a desired workstation on a production line poses numerous difficulties. Tooling and other processing equipment at a workstation present obstacles that must be avoided by the incoming and departing workpieces. After reaching a given workstation, the workpieces must be accurately positioned within the workstation to allow necessary processing operations to be performed. Efficiency and accuracy requirements of modern production lines require that workpiece delivery to a workstation be as rapid and precise as possible.
In many common production lines and other assembly applications, workpieces are transported along an overhead rail, for instance a monorail. Powered roller rail systems move support trolleys or carriages between various workstations. Electrical conductors can be provided along the rail to provide power to the trolley motors. The trolleys carry workpieces along the path defined by the rail, delivering the workpieces to the workstations. To perform a processing operation on a workpiece transported along an overhead rail, often a mechanism must be provided to raise and lower the workpiece with respect to the workstation to properly position the workpiece in the workstation. Prior powered roller rail and trolley systems and devices used to raise and lower workpieces in a workstation include those described in U.S. Pat. Nos. 6,799,673; 9,513,625; and U.S. Patent Application Publication No. 2015/0128719 assigned to the assignee of the present invention and all incorporated herein by reference.
Many prior known mechanisms for raising and lowering a workpiece into the workstation have moved the entire workpiece-laden trolley along with an entire section of the overhead rail. This type of mechanism is complicated in design and prone to wear. For example, joints must be provided between the fixed and moveable rail sections to disengage and re-engage the rail and/or trolley to the main conveyor mechanism. It can be difficult to ensure that the section of rail lowered with the trolley is properly realigned with the fixed rail sections. This negatively impacts the operational capacity of the production or assembly lines, for instance by causing wasteful “down-time” for repairs. In addition to the foregoing disadvantages, many prior known mechanisms cycle at relatively slow speeds, since the weight of the carrier, trolley, and rail must all be borne by the movement mechanism. Consequently, a need exists for a simplified lifting mechanism that meets the efficiency requirements of modern production and assembly lines, and which is simple in operation.